This invention relates to camshafts for internal combustion engines and the like. More particularly, the invention relates to camshafts and a method of making a camshaft in which individually produced cams and journal elements are fastened to a hollow tube by outwardly deforming the tube with a lost mandrel which is left securely in position to form a seal in the tube.
Due to increasing demand for higher performance, lower maintenance and better fuel economy, it is desirable to make automotive camshafts lighter and more durable. Thus camshafts have been developed which have separately produced cam elements for better wear resistance and steel tube for weight saving.
These types of camshafts are manufactured by assembling the individual components, such as cams and journal elements, on a separate, hollow tube and then securing the assembled elements together. However, these assembled camshafts and the methods of making them have many shortcomings which result in time consuming assembly steps, large assembly force requirements and excessive tolerance control. All of these result in more costly manufacture.
U.S. Pat. No. 4,597,367 to Madaffer discloses an assembled camshaft formed of an expandable steel tube and separately hardened cam and journal elements. The elements are secured together by mechanical expansion of the tube. A round forming mandrel is pushed through the tube to expand the tube wall outward to provide a tight engagement fit with the hexagonal openings in the cam and journal elements. The method disclosed in this patent requires a large amount of force since both the inner diameter and outer diameter of the tube is completely expanded. Additionally, after the forming mandrel has been forced through the tube, it must be slowly drawn back through the tube to minimize metal to metal contact. Thus, this method of manufacture requires large amounts of force and time.
Furthermore, if it is desired to seal or plug the hollow tube forming the camshaft, separate manufacturing and assembly steps are required. The closure member must be manufactured with close tolerances so that it will securely fit and seal the hollow deformed camshaft tube. Otherwise, a separate sealing operation such as brazing must be performed. Thus, a camshaft having a plugged tube requires additional manufacturing steps and expensive tolerance control.